1. Field of the Invention
The present invention relates to the construction of a cooling water or coolant jacket formed in a cylinder head of a water-cooled internal combustion engine.
2. Description of the Related Art
Conventionally, known as a cylinder head of a water-cooled internal combustion engine of this type is a cylinder head construction of an internal combustion engine disclosed by JP-A-11-117803. In this cylinder head construction, a rib is provided between adjacent cylinders which connects a circumferential edge portion of an intake valve port of one of the cylinders and a circumferential edge portion of an exhaust valve port of the other cylinder. The rib, which is formed on an upper surface of a lower deck which constitutes a bottom of a coolant jacket in such a manner as to have an angle section, connects to the circumferential edge portion of the inlet valve port on an upstream side of the flow direction of coolant flowing between the cylinders and the circumferential edge portion of the exhaust valve port on a downstream side thereof. Then, the rib so formed deflects the flow direction of the coolant to guide the coolant between circumferential edge portions of a pair of exhaust valve ports so as to attain the cooling of vicinities of the same portions.
Incidentally, in the related art, since the rib formed in such a manner as to protrude from the upper surface of the lower deck connects the circumferential edge portion of the inlet valve port and the circumferential edge portion of the exhaust valve port, there occurs on the back of the rib stagnation in the flow of coolant relative to the flow direction of coolant which flows against the rib on the upper surface of the lower deck and the surface of the circumferential portion of the exhaust valve port, whereby there is caused a problem that the cooling effect becomes deteriorated on the lower deck and the circumferential edge portion of the exhaust valve port which are particularly heated to high temperatures due to the exposure to combustion gases.
The invention was made in view of these situations, and a common object of first to fourth aspects of the invention is to improve the cooling effect of a coolant jacket of an internal combustion engine which has deflecting ribs for directing coolant to exhaust-valve-port side port wall portions whose heat load is high by reducing areas where the stagnation of coolant occurs by the deflecting ribs. Then, an object of the second and fourth aspects of the invention is to improve the cooling effect by preventing the occurrence of the stagnation at the port wall portion on the exhaust-valve-port side. Furthermore, an object of the third aspect of the invention is to improve the rigidity of the cylinder head.
According to the first aspect of the invention, there is provided a cylinder head cooling construction for an internal combustion engine with cylinders and a crankshaft in which a coolant jacket through which coolant is allowed to flow is formed by cylinder walls including bottom walls forming chamber walls of combustion chambers, intake port walls forming intake ports having intake valve ports which are opened and closed by intake valves and exhaust port walls forming exhaust ports having exhaust valve ports which are opened and closed by exhaust valves, and in which deflecting ribs are formed in the coolant jacket between intake-valve-port side port wall portions and exhaust-valve-port side port wall portions which are situated downstream of the intake-valve-port side port wall portions in a flow direction of the coolant in such a manner as to protrude upwardly from the bottom walls for directing the flow of coolant toward the exhaust-valve-port side port wall portions, the cylinder head cooling construction being characterized in that the deflecting ribs for deflecting part of the flow of coolant which flows in a cylinder head center line direction toward the exhaust-valve-port side port wall portions between the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions are formed such that the deflecting ribs leave gaps between at least either the intake-valve-port side port wall portions or the exhaust-valve-port side port wall portions and the deflecting ribs or that the deflecting ribs extend from the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions to leave gaps at intermediate positions thereof for allowing the coolant to flow wall surfaces of the bottom walls, wall surfaces of the intake-valve-port side port wall portions, or wall surfaces of the exhaust-valve-port side port wall portions.
According to the construction of the first aspect of the invention, since the deflecting ribs which protrude upwardly from the bottom walls are formed such that the deflecting ribs leave gaps between at least either the intake-valve-port side port wall portions or the exhaust-valve-port side port wall portions and the deflecting ribs or that the deflecting ribs extend from the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions to leave gaps at intermediate positions thereof for allowing the coolant to flow wall surfaces of the bottom walls, wall surfaces of the intake-valve-port side port wall portions, or wall surfaces of the exhaust-valve-port side port wall portions, the gaps eliminate any risk that the coolant stagnates on the wall surfaces of the bottom walls forming the chamber walls of the combustion chambers, the wall surfaces of the intake-valve-port side port wall portions or the wall surfaces of the exhaust-valve-port side port wall portions. As a result, the following advantage is provided. Namely, since part of the coolant is deflected to flow toward the exhaust-valve-port side port wall portions which have the highest heat load among the walls of the cylinder head which constitute the coolant jacket, the cooling effect on the exhaust-valve-port side port wall portions is improved. Moreover, being different from the continuous ribs according to the prior art, the coolant flowing through the gaps eliminates the occurrence of stagnation of coolant on the wall surfaces of the bottom walls, the wall surfaces of the intake-valve-port side port wall portions and the wall surfaces of the exhaust-valve-port side port wall portions at the portions where the gaps are formed. Furthermore, part of the coolant flowing in from the gaps flows around to the back of the deflecting ribs, and this reduces further areas where the stagnation in the flow of coolant is generate, whereby the areas where the coolant stagnates due to the deflecting ribs are reduced, the cooling effect on the bottom walls, the intake-valve-port side port wall portions or the exhaust-valve-port side port wall portion being thereby improved.
According to the second aspect of the invention, there is provided a cylinder head cooling construction for an internal combustion engine as set forth in the first aspect of the invention, wherein the deflecting ribs are formed to extend from the intake-valve-port side port wall portions, and wherein the gaps are designed to allow the coolant to flow on the wall surfaces of the exhaust-valve-port side port wall portions between the exhaust-valve-port side port wall portions and the deflecting ribs.
According to the construction of the second aspect of the invention, the following advantage is provided. Namely, since the gaps are formed between the exhaust-valve-port side port wall portions and the deflecting ribs, part of the coolant is deflected to flow toward the exhaust-valve-port side port wall portions which have the highest heat load among the walls of the cylinder head which constitute the coolant jacket, whereby the cooling effect on the exhaust-valve-port side port wall portions is improved. Moreover, being different from the continuous ribs according to the prior art, the coolant flowing through the gaps eliminates the occurrence of stagnation of coolant on the wall surfaces of the exhaust-valve-port side port wall portions at the portions where the gaps are formed. Furthermore, part of the coolant flowing in from the gaps flows around to the back of the deflecting ribs, and this reduces further areas where the stagnation in the flow of coolant is generate, whereby the areas where the coolant stagnates due to the deflecting ribs are reduced, the cooling effect on the exhaust-valve-port side port wall portion being thereby improved. Thus, the portions having a high heat load can be cooled effectively.
According to the third aspect of the invention, there is provided a cylinder head cooling construction for an internal combustion engine as set forth in the first or second aspect of the invention, wherein the internal combustion engine is a multi-cylinder internal combustion engine, wherein the deflecting rib is formed between the intake-valve-port side port wall portion of one of two cylinders of said cylinders which are contiguous with each other in the cylinder head center line direction and the exhaust-valve-port side port wall portion of the other cylinder, and wherein the deflecting ribs protrude upwardly from the bottom wall to connect to a central rib which extend in the cylinder head center line direction between end portions of the cylinder head.
According to the construction of the third aspect of the invention, in addition to the advantages provided by the cited aspects of the invention, the following advantage is provided. Namely, since the central rib is provided on the bottom wall of the cylinder head which protrudes upwardly from the bottom wall and extends in the cylinder head center line direction between the end portions of the cylinder head, the coolant which flows between the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions of the cylinder head is straightened along the cylinder head center line direction to flow to the downstream side, whereby the chamber wall of the combustion chamber, the intake-valve-port side port wall portion and the exhaust-valve-port side port wall portion of each cylinder can be cooled substantially equally with the coolant so flowing. In addition, the provision of the central rib and the deflecting ribs which connect to the central rib can contribute to making the entirety of the cylinder head more rigid.
According to the fourth aspect of the invention, there is provided a cylinder head cooling construction for an internal combustion engine with cylinders and a crankshaft in which a coolant jacket through which coolant is allowed to flow is formed by cylinder walls including bottom walls forming chamber walls of combustion chambers, upper walls, intake port walls forming intake ports having intake valve ports which are opened and closed by intake valves and exhaust port walls forming exhaust ports having exhaust valve ports which are opened and closed by exhaust valves, and in which deflecting ribs are formed in the coolant jacket between intake-valve-port side port wall portions and exhaust-valve-port side port wall portions which are situated downstream of the intake-valve-port side port wall portions in a flow direction of the coolant in such a manner as to protrude upwardly from the bottom walls for directing the flow of coolant toward the exhaust-valve-port side port wall portions, the cylinder head cooling construction being characterized in that the deflecting ribs for deflecting part of the flow of coolant which flows in a cylinder head center line direction toward the exhaust-valve-port side port wall portions between the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions are formed such that the deflecting ribs extend downwardly from the upper walls and extend toward the intake-valve-port side port wall portions and the exhaust-valve-port side port wall portions to leave gaps between lower end portions of the deflecting ribs and the exhaust-valve-port side port wall portions and the bottom walls for allowing the coolant to flow on wall surfaces of the exhaust-valve-port side port wall portions and wall surfaces of the bottom walls.
According to the construction of the fourth aspect of the invention, the following advantage is provided. Namely, since the lower end portions of the deflecting ribs which protrude downwardly from the upper walls form the gaps between the exhaust-valve-port side port wall portions and the bottom walls and themselves for allowing the coolant to flow on the respective wall surfaces of the bottom walls and the exhaust-valve-port side port wall portions, there is no risk that the coolant stagnates on the respective wall surfaces of the bottom walls that form the chamber walls of the combustion chambers and the exhaust-valve-port side port wall portions. As a result, the following advantage is provided in turn. Namely, since part of the coolant is deflected to flow toward the exhaust-valve-port side port wall portions which have the highest heat load among the walls of the cylinder head which constitute the coolant jacket, the cooling effect on the exhaust-valve-port side port wall portions is improved. Moreover, the coolant flowing through the gaps eliminates the occurrence of stagnation of coolant on the wall surfaces of the bottom walls and the wall surfaces of the exhaust-valve-port side port wall portions at the portions where the gaps are formed, whereby the areas where the coolant stagnates due to the deflecting ribs are reduced, the cooling effect on the bottom walls and the exhaust-valve-port side port wall portion being thereby improved. Thus, the portions having a high heat load can be cooled effectively.
Note that as used herein, the term xe2x80x9cviewed from the topxe2x80x9d means viewing from a centrally axial direction of a cylinder bore, and the terms xe2x80x9cintake-valve-port side port wall portionxe2x80x9d and xe2x80x9cexhaust-valve-port side port wall portionxe2x80x9d mean, respectively, an intake-port wall and an exhaust-port wall which are included within the range of the cylinder bore as viewed from the top. In addition, the term xe2x80x9ccylinder-head center linexe2x80x9d means a straight line in the cylinder head when viewing from the centrally axial direction of the cylinder, an imaginary plane including central axes of the cylinder bores and the rotational axis of the crankshaft or an imaginary plane including the central axes of the cylinder bores and being parallel to the rotational axis of the crankshaft. Additionally, the terms xe2x80x9cintake sidexe2x80x9d and xe2x80x9cexhaust sidexe2x80x9d mean, respectively, a side of the cylinder head where inlet ports for the intake ports are situated and the other side of the cylinder where outlet ports for the exhaust ports are situated, relative to the imaginary planes.